High contamination risks of thallium and associated metal(loid)s in fluvial sediments from a steel-making area and implications for environmental management.

Thallium (Tl) is an uncommon toxic element, with an even greater toxicity than that of As, Hg and Cd. Steel-making industry has been identified as an emerging new significant source of Tl contamination in China. This paper presents a pilot investigation of the contamination and geochemical transfer of Tl and associated metal(loid)s in river sediments affected by long-term waste discharge from the steel-making industry. The results uncovered an overall Tl contamination (1.96 ± 0.42 mg/kg) across a sediment profile of approximately 1.5 m in length, even 10 km downstream the steel plant. Highly elevated contents of Pb, Cu, Cd, Zn and Sb were found in the fluvial sediments, displaying strong positive correlations with Tl contents. Elevated levels of geochemically mobile Tl as well as Cd, Zn, Cu and Pb occurred in the fluvial sediments, signifying anthropogenic imprints from steel production activities at high temperature. Levels of contamination and ecological risk were calculated to be moderate to considerable for Tl, Cu, Zn and high to very high for Cd, Pb, Sb. The results highlight that there is a great challenge in view of potentially considerable Tl pollution due to continuous massive steel production in many other parts of China. It is high time to initiate process-based management of Tl contamination control for the ambient aquifer system in the steel-making area.